nfp: store device pointer for the fastpath

We really only need the device pointer on the fast path, stash it at
the beginning of the adapter structure and move pci_dev pointer down.
This saves up a few lines of code.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>